Gate device over strained fin structure

ABSTRACT

A method for forming a semiconductor device includes forming a fin structure on a substrate, forming a shallow trench isolation region adjacent the fin structure so that an upper portion of the fin structure is exposed, forming a dummy gate over the exposed fin structure, forming an interlayer dielectric layer around the dummy gate, removing the dummy gate to expose the fin structure, and after removing the dummy gate, introducing a strain into a crystalline structure of the exposed fin structure.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 14/062,993, issuing as U.S. Pat. No. 9,590,104entitled “GATE DEVICE OVER STRAINED FIN STRUCTURE,” filed Oct. 25, 2013,of which is hereby incorporated by reference in its entirety.

BACKGROUND

Integrated circuits may be formed using various photolithographictechniques. Such techniques are used to form different types ofcomponents and devices including transistors. One type of transistor isa Metal Oxide Semiconductor Field Effect Transistor (MOSFET). MOSFETdevices use a gate terminal, a source terminal, and a drain terminal.Among other functions, the MOSFET device may act as a switch. Whenacting as a switch, the signal applied to the gate terminal will eithercause the MOSFET device to allow or prohibit current flow between thesource and drain terminals.

The source and drain components of a MOSFET device typically includedoped regions of a semiconductor substrate or material. The channelbetween the source and drain regions underneath a gate device may beshaped like a fin that passes through the bottom portion of the gatestructure in a perpendicular manner. Transistors that use fin shapedchannels are sometimes referred to as finFETs.

In some cases, it can be beneficial to introduce a strain into the finstructures. Straining may be done by injecting a type of semiconductorwith a different lattice constant than the original semiconductormaterial. For example, a silicon fin may be doped withsilicon-germanium. This will cause a strain in the crystalline structureof the fin. If done properly, this can increase carrier mobility andthus increase the efficiency of the fin. This straining process,however, can be harmed by various processes such as thermal annealing.Thermal annealing is part of forming source and drain regions. It isdesirable form strained structures that will not be adversely affectedby various processes such as thermal annealing.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIGS. 1A-1F are diagrams showing an illustrative method of forming agate device with strained fin structures, according to one example ofprinciples described herein.

FIGS. 2A-2G are diagrams showing an illustrative method of forming agate device with epitaxial grown strained fin structures, according toone example of principles described herein.

FIG. 3 is a diagram showing a top view of an illustrative gate deviceover strained fin structures, according to one example of principlesdescribed herein.

FIG. 4 is a flowchart showing an illustrative method for forming a gatedevice over strained fin structures, according to one example ofprinciples described herein.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

FIGS. 1A-1F are diagrams showing an illustrative method of forming agate device with strained fin structures. According to the presentexample, a number of fin structures 104 are formed onto a substrate 102.For purposes of discussion, the fin structures 104 include an upperportion 106 and a lower portion 107.

According to the present example, the fin structures 104 may be formedusing standard semiconductor fabrication processes. Such processes mayinclude deposition, etching, photolithography, etc. In this example, twofin structures 104 are associated with a single gate device. In someexamples, however, there may be one fin structure 104 associated with agate device. In a further example, there may be more than two finstructures 104 associated with a single gate device.

According to the present example, an isolation structure 108 is formedbetween the fin structures 104. The isolation structure 108 may be, forexample, a Shallow Trench Isolation (STI) structure. The isolationstructure 108 is a dielectric material designed to isolate variousfeatures from nearby features. For examples, the isolation structure 108may prevent electric current flowing through one fin structure fromflowing to another fin structure 104. The isolation structure 108 isformed around the lower portion 107 of the fin structures. The upperportion 106 of the fin structures 104 remains exposed.

FIG. 1B is a diagram showing the formation of dummy gate devices 110,111 over the fin structures. According to the present example, dummygates 110, 111 are formed over the upper portion 106 of the finstructures 104. The two dummy gates 110, 111 each correspond to twodifferent fin structures 104. In one example, the first dummy gate 110may be associated with a PMOS (p-type Metal Oxide Semiconductor)transistor and the second dummy gate 111 may be associated with an NMOS(n-type Metal Oxide Semiconductor) transistor.

According to the present example, sidewall spacers 112 are formed on theedges of the dummy gates 110, 111. The sidewall spacers 112 may beformed using various deposition processes or epitaxial growth processes.The sidewall spacers 112 are designed to stay in place even after thedummy gates 110, 111 are removed, which will be discussed in more detailbelow.

FIG. 1C illustrates the formation of an interlayer dielectric (ILD)layer 114. According to the present example, the ILD layer 114 is formedto surround the dummy gates 110, 111. In one example, the ILD layer 114is formed partially over the dummy gate devices 110, 111. A ChemicalMechanical Polishing (CMP) process, however, can remove part of the ILDlayer 114 to expose the top of the dummy gates 110, 111. The ILD layer114 is used to isolate components of adjacent layer from each other.

FIG. 1D illustrates the removal of the dummy gates 110, 111 to exposethe upper portion 106 of the fin structures 104. Removal of the dummygates 110, 111 may be done through a selective etching process. Aselective etching process is designed to remove one type of materialwhile leaving other types of material intact. For example, the etchingprocess may be designed to remove the dummy gate material but leave theILD layer 114 and the sidewall spacers 112 intact. Removal of the dummygates 110, 111 leaves two openings 116 into which real gates may besubsequently placed.

FIG. 1E is a diagram showing an illustrative straining process.According to the present example, the upper portions 106 of some of thefin structures 104 are strained. This may be done by a variety ofmethods. In one example, the upper portions 106 of the fin structures104 are doped with a semiconductor material having a different latticeconstant than the original semiconductor material. For example, if thefin structures 104 are made of silicon, then the fin structures 104 maybe doped with germanium which has a different lattice constant.Alternatively, the fin structures 104 may be doped with a type III-Vsemiconductor material.

The straining material may be introduced by various doping processes. Inone example, the straining material is introduced using ionimplantation. In one example, the straining material is introduced usinga diffusion process.

In some examples, the upper portion 106 of the fin structures 104 may beremoved and then replaced with an epitaxial strained semiconductor. Anepitaxial process may be used to selectively grow the upper portions 106of the fin structures with the strained material on the top of the lowerportions 107 of the fin structures 104. Other methods may be used tointroduce the straining material are contemplated.

In this example, the fin structures 104 within the first opening 116 arestrained but the fin structures 104 of the second opening 117 are notstrained. In some cases, it may be desirable to introduce strain intoone gate and not the other gate because the gates may have differentdesign purposes. For example, one gate may be for an NMOS device whilethe other gate may be for a PMOS device. In some cases, the finstructures for multiple openings 116, 117 may be strained differently.The different straining processes may be based on the type of transistorfor which the gate will be used.

As mentioned above, the processes that are used to strain the finstructures may be harmful to various metal structures including metalgates. Additionally, other doping processes are performed on thesemiconductor substrate 102. For example, the source and drain regionsare formed using various doping processes. A thermal annealing processis then performed on the source and drain regions. This process can beharmful to the strained material. Thus, the strained material is formedafter this annealing process. The annealing process is also typicallyperformed with the dummy gates in place. Thus, the straining processtakes place after the dummy gates have been removed and before the metalreplacement gates are formed.

FIG. 1F illustrates formation of the replacement metal gates 122, 123.According to the present example, a high-k dielectric layer 118 isformed over the upper portions 106 of the fin structures 104 as well asthe rest of the opening 116 left by removal of the dummy gates 110, 111.The high-k dielectric layer 118 is commonly used with metal gatestructures as insulation between the metal material and thesemiconductor material.

After the high-k material 118 is in place, the metal gates 122, 123 canthen be formed. The metal gates 122, 123 may be formed by deposition ofa metal material into the openings 116 left by removal of the dummygates 110, 111. A CMP process may then be used to smooth the surface ofthe ILD layer 114.

FIGS. 2A-2G are diagrams 200 showing an illustrative method of forming agate device with strained fin structures 204. FIG. 2A is a diagramshowing formation of an isolation structure 208 around fin structures204. The fin structures 204 are formed onto a substrate 202. The finstructures 204 include an upper portion 206 and a lower portion 207.

In the present example, the isolation structure 208 is formed such thatit covers both the upper portions 206 and the lower portions 207 of thefin structures 204. In some examples, a CMP process may be used tosmooth the surface of the isolation structure 208. The isolationstructure 208 may be an STI structure.

FIG. 2B is a diagram showing the formation of dummy gates 210, 211.According to the present example, the dummy gates 210, 211 shown are notas tall as the dummy gates 110, 111 shown in FIG. 1. This is because theisolation structure 208 is higher than the isolation structure 108 ofFIG. 1.

After the dummy gates 210, 211 are formed, sidewall spacers 212 areformed on the sides of the dummy gates 210, 211. The height of thesesidewall spacers 212 is also less than the height of the sidewallspacers 112 of FIG. 1. After the sidewall spacers 212 are formed on thedummy gates 210, 211, an ILD layer 214 is formed to surround the dummygates 210, 211. Again, a CMP process may be used to smooth the surfaceof the ILD layer 214 and the dummy gates 210, 211.

FIG. 2C illustrates the removal of the dummy gates 210, 211, to leaveopenings 216. The dummy gates 210, 211 may be removed through variousprocesses such as selective etching. Specifically, a selective etchingprocess that removes only the dummy gate material while leaving the ILDlayer 214 and the sidewall spacers 212 intact may be used.

FIG. 2D illustrates the removal of the upper portions 206 of the finstructures 204. Again, this may be done through a selective etchingprocess that removes only the fin structure material while leaving theILD layer 214, the sidewall spacers 212, and the isolation structure 208intact. Removal of the upper portions 206 of the fin structures leavesbehind a set of trenches 218. These trenches 218 can then be used toform new upper portions of the fin structures 204.

FIG. 2E illustrates the formation of strained upper portions 220 of thefin structures 204 in the trenches 218 left by removal of the originalupper portions 206 of the fin structures 204. The strained upperportions 220 may be formed through an epitaxial growth process that isdesigned to grow a crystalline structure from the semiconductor materialforming the lower portions 207 of the fin structures 204. Because thestrained upper portions 220 are grown in the trenches 216, the epitaxialgrowth process is constrained to the desired dimensions. Thus, a betterstrained fin structure 204 is formed.

The strained nature of the strained upper portions 220 of the finstructures 204 results from growing a crystalline structure withdifferent elements having different lattice constants. For example, thestrained upper portions 220 of the fin structures 204 may be made ofsilicon and germanium. In some examples, other semiconductor materialssuch as type III-V semiconductor materials may be used.

FIG. 2F is a diagram showing removal of a portion of the isolationstructure 208 to expose the strained upper portions 220 of the finstructures 204. This forms a complete opening 222 for the replacementgates. The removal process may be done through a selective etchingprocess that is designed to remove the isolation structure 208 whileleaving the strained upper portions 220 of the fin structures 204, theILD 214, and the sidewall spacers 212 intact.

FIG. 2G is a diagram showing the final gate structures formed into thecomplete openings 222. According to the present example, a high-kdielectric layer 224 is formed over the upper portions 220 of the finstructures 204 as well as the rest of the complete opening 222 left byremoval of the dummy gates 210, 211 and isolation material 208. Thehigh-k dielectric layer is 224 commonly used with metal gate structures226, 227 as insulation between the metal material and the semiconductormaterial.

After the high-k material is in place, the metal gates 226, 227 can thenbe formed. The metal gates 226, 227 may be formed by deposition of ametal material into the complete openings 222. A CMP process may then beused to smooth the surface of the metal gates and ILD layer 214.

In the present example, performance of the above described processresults in a structure in which the border 228 between the ILD 214 andthe isolation structure 208 is between the top and bottom of the metalgates 226, 227. Additionally, the sidewall spacers 212 adjacent themetal gates 226, 227 extend down to the border 228 instead of extendingthe entire height of the metal gates 226, 227. The border 228 alsocorresponds with the height of the strained upper portions 220 of thefin structures 204. While in this example, the border 228 is shown inthe exact middle between the top and bottom of the metal gates 226, 227,other locations of the border between the top and bottom of the metalgates 226, 227 are contemplated. For example, the border 128 may becloser to the top or closer to the bottom of the metal gates 226, 227.

FIG. 3 is a diagram showing a top view of an illustrative gate device300 over strained fin structures 302. According to the present example,the gate device 300 is formed over four separate fin structures 302. Thefin structures 302 run perpendicular to the gate structure 306 andparallel to each other. The regions 304 of the fin structures 302 thatare strained lay underneath the gate structure 306. The remainingportions of the fin structures 302 may remain unstrained. The strainedregions 304 are shown with dashed lines because they are positionedunderneath the gate structure 306.

FIG. 4 is a flowchart showing an illustrative method for forming a gatedevice over strained fin structures. According to the present example,the method includes a step for forming 402 a fin structure on asubstrate. The method further includes a step for forming 404 a shallowtrench isolation region adjacent the fin structure so that an upperportion of the fin structure is exposed. The method further includes astep for forming 406 a dummy gate over the exposed fin structure. Themethod further includes a step for forming 408 an interlayer dielectriclayer around the dummy gate. The method further includes a step forremoving the dummy gate 410 to expose the fin structure. The methodfurther includes a step for, after removing the dummy gate, introducing412 a strain into a crystalline structure of the exposed fin structure.

According to certain illustrative examples, a method for forming a gatedevice over a strained fin structure includes forming a fin structure ona substrate, forming a shallow trench isolation region adjacent the finstructure so that an upper portion of the fin structure is exposed,forming a dummy gate over the exposed fin structure, forming aninterlayer dielectric layer around the dummy gate, removing the dummygate to expose the fin structure, and after removing the dummy gate,introducing a strain into a crystalline structure of the exposed finstructure.

According to certain illustrative examples, forming a first and secondfin structure onto a substrate, forming an isolation structure betweenthe fin structures, applying a Chemical Mechanical Polishing (CMP)process to the substrate, forming a first dummy gate over the first finstructure and a second dummy gate over the second fin structure, formingan interlayer dielectric layer around the first and second dummy gates,removing the first and second dummy gates, after removing the first andsecond dummy gates, selectively removing a top portion of the first andsecond fin structures, and in one of the openings left by removing thefirst and second fin structures, forming a strained fin structure.

According to certain illustrative examples, a semiconductor deviceincludes at least one fin structure formed onto a substrate, anisolation structure surrounding a lower portion of the fin structure, ahigh-k metal gate formed over the fin structure such that the finstructure extends into the gate structure, and an interlayer dielectricstructure surrounding the metal gate. The border between the isolationstructure and the interlayer dielectric structure is positioned betweena top and a bottom of the metal gate.

It is understood that various different combinations of the above-listedembodiments and steps can be used in various sequences or in parallel,and there is no particular step that is critical or required.Additionally, although the term “electrode” is used herein, it will berecognized that the term includes the concept of an “electrode contact.”Furthermore, features illustrated and discussed above with respect tosome embodiments can be combined with features illustrated and discussedabove with respect to other embodiments. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention.

The foregoing has outlined features of several embodiments. Those ofordinary skill in the art should appreciate that they may readily usethe present disclosure as a basis for designing or modifying otherprocesses and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those of ordinary skill in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method for forming a semiconductor device, themethod comprising: forming a first and second fin structure onto asubstrate; forming an isolation structure between the fin structures;applying a Chemical Mechanical Polishing (CMP) process to the substrateincluding the first and second fin structures; after applying the CMP,forming a first dummy gate over the first fin structure and a seconddummy gate over the second fin structure; forming an interlayerdielectric layer around the first and second dummy gates; removing thefirst and second dummy gates; after removing the first and second dummygates, selectively removing a top portion of the first and second finstructures; and in one of the openings left by removing the first andsecond fin structures, forming a strained fin structure.
 2. The methodof claim 1, further comprising, removing an upper portion of theisolation structure to expose the upper portion of the strained finstructure.
 3. The method of claim 2, further comprising, forming ahigh-k material over the strained fin structure.
 4. The method of claim3, further comprising, forming a first and second metal gate over thehigh-k material.
 5. The method of claim 1, further comprising, formingstrained fin structures in both openings left by removing the topportion of the first and second fin structures.
 6. The method of claim1, further comprising, forming additional fin structures associated withboth the first and second dummy gates.
 7. The method of claim 1, furthercomprising forming sidewall spacers on sides of the first and seconddummy gates before removing the first and second dummy gates.
 8. Themethod of claim 1, wherein the isolation structure is a shallow trenchisolation (STI) structure.
 9. The method of claim 1, wherein the firstfin structure is strained differently than the second fin structure. 10.A method for forming a semiconductor device, the method comprising:forming a fin structure extending from a substrate; forming an isolationstructure adjacent the fin, wherein a first portion of the isolationstructure is on a first side of the fin structure and a second portionof the isolation structure is on a second side of the fin structureopposite the first side; forming a dummy gate over the fin structure andthe first and second portions of the isolation structure; after removingthe dummy gate, selectively etching a top portion of the fin structureto form a trench between the first and second portions of the isolationstructure; epitaxially growing a semiconductor material in the trench;and forming a gate structure over the epitaxially grown semiconductormaterial.
 11. The method of claim 10, wherein the dummy gate is formedon a planar surface defined by the fin structure and the first andsecond portions of the isolation structure.
 12. The method of claim 10,wherein the eptiaxially growing the semiconductor material includesgrowing silicon and germanium.
 13. The method of claim 10, furthercomprising: after epitaxially growing the semiconductor material,selectively etching the first and second portions of the isolationstructure such that the epitaxially grown semiconductor material forms afin portion extending above a first top surface of the etched isolationstructure.
 14. The method of claim 13, wherein a second top surface ofthe isolation structure after the etching lies above the first topsurface and is coplanar with a portion of the gate structure.
 15. Themethod of claim 14, wherein the forming the gate structure includesforming the gate structure extending above a height of the second topsurface of the isolation structure.
 16. A method for forming asemiconductor device, the method comprising: providing a substratehaving a fin structure and an isolation structure disposed on thesubstrate; etching a top portion of the fin structure to form a trenchhaving sidewalls defined by the isolation structure and a bottom surfacedefined by a remaining portion of the fin structure; epitaxially growinga semiconductor material in the trench to form an upper fin portion overthe remaining fin portion; after epitaxially growing the semiconductormaterial, recessing a first region of the isolation structure adjacentthe upper fin portion, while a second region of the isolation structurespaced a distance from the upper fin portion underlies a dielectriclayer; and forming a gate structure over the upper fin portion and therecessed first region of the isolation structure.
 17. The method ofclaim 16, wherein the epitaxially growing the semiconductor materialforms the upper fin portion of a different composition than theremaining fin portion.
 18. The method of claim 16, wherein theepitaxially growing the semiconductor material includes forming theupper fin portion including silicon and germanium.
 19. The method ofclaim 16, further comprising: performing a chemical mechanical polish onthe substrate having the fin structure and the isolation structure priorto etching the top portion of the fin structure.
 20. The method of claim16, wherein the forming the gate structure includes depositing a high-kdielectric material on a top surface and opposing sidewalls of the upperfin portion and on at least two differently oriented surfaces of theisolation structure.